Display Zoom information
Blender doesn't offer a way to show the zoom level but we can use python to display it if we want.

The simplest way is to add a panel -

import bpy
import math

class Image_PT_zoom(bpy.types.Panel):
    bl_idname = "Image_PT_zoom"
    bl_label = "Image Zoom"
    bl_space_type = 'IMAGE_EDITOR'
    bl_region_type = 'UI'

    def draw(self, context):
        zoom = context.space_data.zoom[0]*100
        zoom_h = context.space_data.zoom[1]*100
        if math.isclose(zoom,zoom_h,rel_tol=0.001):
            self.layout.label(text="{:.1f}%".format(zoom))
        else:
            self.layout.label(text="Width:  {:.1f}%".format(zoom))
            self.layout.label(text="Height: {:.1f}%".format(zoom_h))

def register():
    bpy.utils.register_class(Image_PT_zoom)

def unregister():
    bpy.utils.unregister_class(Image_PT_zoom)

register()


You can find this as an addon here.